This invention relates to a tensioning arrangement for transmission belts.
One tension arrangement of this type is disclosed in U.S. Pat. No. 4,557,707. This reference discloses a tension roller mounted at one end of the pivot arm with the pivot arm rotatably mounted on a flange affixed to a motor block. The tension of the roller against the transmission belt is adjusted by a torsion spring. An annular space is defined by an annular side surface of the pivot arm and the flange, and a friction element is positioned in the annular space. The side surface of the friction element is a friction surface that contacts the annular side surface of the pivot arm with rubbing contact. The friction surface extends over the whole circumference of the friction element and ensures a uniform support and a minimal constant displacement. Pivot movement of the pivot arm which is caused by vibration of the transmission belt or by impulse shock acting opposite the tension direction is damped by energy loss by the friction element. An equivalent action can be produced by the cylindrical friction surface of a similar friction element, if corresponding bore or outer surfaces are provided on the pivot arm and on a fixed part. A difference exists, however, between the above mentioned vibration and the impulse shock in the pivot direction. While the vibration oscillates mostly with higher frequencies and in a relataively small angular region, impulse shock occurs sporadically and effects a pivotal movement in a larger angular region. In the above described tension arrangement, both of these known influences are damped in the same manner, whereby in critical situations the transmission belt can completely lift off from the tension roller. In this case the tension arrangement returns too slowly in the tension direction after greater excursions resulting from an impulse shock opposite the tension direction, as a result of stronger damping. While arrangements are specifically provided which produce a damping force that is dependent upon the pivot position, these arrangements have no influence on above discussed detrimental action.